From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D523BC433E0 for ; Mon, 15 Feb 2021 19:52:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A0E1164DFD for ; Mon, 15 Feb 2021 19:52:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230195AbhBOTwm (ORCPT ); Mon, 15 Feb 2021 14:52:42 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38298 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230097AbhBOTwi (ORCPT ); Mon, 15 Feb 2021 14:52:38 -0500 Received: from mail-ed1-x529.google.com (mail-ed1-x529.google.com [IPv6:2a00:1450:4864:20::529]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7DC3EC061574 for ; Mon, 15 Feb 2021 11:51:58 -0800 (PST) Received: by mail-ed1-x529.google.com with SMTP id df22so9628716edb.1 for ; Mon, 15 Feb 2021 11:51:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=soleen.com; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ggXAchxe/nqZ+4UDDGVutSsPhwxIlT0f1nO/trNU9oc=; b=IarEwOMOZA33L50oHF3AETzMXemhi0EnToMfhtmZUS8KKm/d0nN+tkOx4xdwD2VTdn WD5BVHnFcSLwHfXjAnYDdhNkNAP7SCxaxnKm8qQAV1i64056rPwLJJ2j2pU0zNNaRvHw 43CyDY40W/dharZ3Two4gbZkV6v6WUSmnsu85LWL+H6lNJTpggZFoR/auGcAE8vGCe6F J46nC7kFBtHIUHx+W8Ns6SLSt2Va0IKY/ZrXVAgVRFl0WqvnxM+weHG1wBeWRNHtC5ph 3i1TeyBzgvHMLDdcE3N8dvJB/qdfF0OarRY3HS4CNooxK6aOlWAiqLGxkyfsnlXY2m+3 3H/Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=ggXAchxe/nqZ+4UDDGVutSsPhwxIlT0f1nO/trNU9oc=; b=MxWu8C+PUaQUcawuqzsNScF/LWxIDu3kCngHb/nTHPWRnS+hHFOaBGkfX/utCEjqOU BXSCAzaxifWe3DkWUawtKIg1nkxKng0aIN17Q2U+R5Mv6116SeWU7XP8kTQnkSa1WUlU nFKIvph5/z5wCzobUnja3zz0TfeeJIBoSjvw44fc61GwPZOUez5Zx8dcYWFhZ3UD2iQ1 GCR4DVTWDwWKwCN1NgKdnKwoYiGx8oVuq6fUG053gOkWo/JwRnxRZJ21WDxhU6YPsEQN eTKK8SA2qQi8WLZeNwhM7GzoDwU9mPpmNxuBHyxPSW6n0VaUcIrnS/VrZpMsGBP9Bn59 doSQ== X-Gm-Message-State: AOAM532t/vUOL5SYmBCBP63HSttfJ/TGk2+rGIvhg6L492mVMG198GSL DPO31gCWwpDsnubq+TojyUxHQA8yR6c4MsYsVsxPgg== X-Google-Smtp-Source: ABdhPJyof1WMeYuO/LOIuwozPZ/M/dMJEhGnpPp9NrjZXVqoSJFYUy5W8dTWP0sEIEjNai5f72V89i+osUosOBSYxh8= X-Received: by 2002:a05:6402:3508:: with SMTP id b8mr17395465edd.341.1613418717238; Mon, 15 Feb 2021 11:51:57 -0800 (PST) MIME-Version: 1.0 References: <20210215192237.362706-1-pasha.tatashin@soleen.com> <20210215192237.362706-2-pasha.tatashin@soleen.com> In-Reply-To: From: Pavel Tatashin Date: Mon, 15 Feb 2021 14:51:21 -0500 Message-ID: Subject: Re: [PATCH v2 1/1] arm64: mm: correct the inside linear map boundaries during hotplug check To: Ard Biesheuvel Cc: Tyler Hicks , James Morris , Catalin Marinas , Will Deacon , Andrew Morton , Anshuman Khandual , Mike Rapoport , Logan Gunthorpe , Linux ARM , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 15, 2021 at 2:34 PM Ard Biesheuvel wrote: > > On Mon, 15 Feb 2021 at 20:30, Pavel Tatashin wrote: > > > > > Can't we simply use signed arithmetic here? This expression works fine > > > if the quantities are all interpreted as s64 instead of u64 > > > > I was thinking about that, but I do not like the idea of using sign > > arithmetics for physical addresses. Also, I am worried that someone in > > the future will unknowingly change it to unsigns or to phys_addr_t. It > > is safer to have start explicitly set to 0 in case of wrap. > > memstart_addr is already a s64 for this exact reason. memstart_addr is basically an offset and it must be negative. For example, this would not work if it was not signed: #define vmemmap ((struct page *)VMEMMAP_START - (memstart_addr >> PAGE_SHIFT)) However, on powerpc it is phys_addr_t type. > > Btw, the KASLR check is incorrect: memstart_addr could also be > negative when running the 52-bit VA kernel on hardware that is only > 48-bit VA capable. Good point! if (IS_ENABLED(CONFIG_ARM64_VA_BITS_52) && (vabits_actual != 52)) memstart_addr -= _PAGE_OFFSET(48) - _PAGE_OFFSET(52); So, I will remove IS_ENABLED(CONFIG_RANDOMIZE_BASE) again. I am OK to change start_linear_pa, end_linear_pa to signed, but IMO what I have now is actually safer to make sure that does not break again in the future.